Polarised light microscopy has been used to assess the physical form of over 800 compounds whose aqueous solubility has been measured in a solubility assay in a drug discovery setting. Analysis of the data indicates the presence of a wide range of physical forms although encouragingly many compounds do appear to be in a crystalline or semi-crystalline form. Approximately 15% of the compounds were identified as remaining in an amorphous state. For these compounds there is a high risk that the solubility value generated will be an over-estimate of the true solubility of the compound.